Mower ran fine "Old Murray 3.5 B&S" Took blade off now wont start. Do they actually need the drag from the blade to run? I dont see how its possible but I have a mower that wont run without the blade and I am stumped.

Steve

06-29-2010, 02:01 PM

Thats a new one to me. As a test, I would put the blade back on and see if it starts then, but I can't imagine that being the case.

jasonw

07-01-2010, 02:01 PM

Steve. It ran fine before I took the blade off. It just confuses me as to why it would not run without the blade. Its not like its got some sort of safety device or anything preventing it. I can understand if it were some top of the line expensive machine but its just a cheap $69.99 Murray mower.

robert brooks

07-02-2010, 09:29 PM

when you took the blades off, how did you do it ? did you turn the mower upside down or on its side? may have flooded carb or caused floats to stick , or possibly fouled plug with oil if rings are worn. remove plug and check. hope this helps

StartALawnCareBusiness

07-03-2010, 05:02 PM

You are correct. The mower will not start without the blade. If you try to start the mower without the blade you will likely get a compression kickback. I know this from personal experience. I tried to start a 5.5 hp Murray lawnmower after taking the blade off to sharpen it. The compression jolt was so strong that it ripped the cord out of my hand. Unfortunately, the starter handle slammed into my chest. It felt like a horse had kicked me.

I took it to a lawn mower shop to see what was wrong. After checking it out, the guy looked at me like I was a complete idiot. "It won't start like that. The blade times the motor." Gee, thanks Mr. Lawn Mower repair guy.

I have a cheap mower from Wal-Mart it runs without a blade I found that out on accident I forgot to put it back on couldn't figure out why it wasn't cutting family got a good laugh out of it

LawnMoore

07-27-2010, 01:21 AM

I have a cheap mower from Wal-Mart it runs without a blade I found that out on accident I forgot to put it back on couldn't figure out why it wasn't cutting family got a good laugh out of it

Oh man, thats was a good one i bet :D It made me chuckle as well.

I bet you were really grinding the gears trying to figuere that out at first, lol

Eugbug

03-12-2014, 04:41 AM

Lots of mowers just have an aluminum flywheel which is relatively light, although some mowers have cast iron flywheels.
The blade actually forms part of the flywheel system. If you are familiar with mechanics (the physics of forces and motion), what the blade actually does is increase the moment of inertia. Its not just the added weight but also the larger diameter which increases moment of inertia. So when you pull the cord and then stop pulling, the extra inertia provided by the blade causes the engine to keep spinning and makes for better starting.

kslawn

03-12-2014, 09:57 AM

That blows. I wander what I can use. It has to be a lay down motor.
What kind of project are you doing? you said you had to lay the motor down??? Please explain.......

Just for Cuts

03-12-2014, 10:10 AM

Nearly all newer small mowers don't have a throttle control. They are designed to be primed, started and they go to redline. Running it without the blade doesn't give it the momentum to complete the 4 cycles. That combined with the smaller, lighter flywheels makes it kick back because it simply too light to maintain the direction of rotation you're pulling it and the fuel being metered into it is more than required to just idle it. If you were able to lock the throttle linkage to an idle position (it will run like crap because these carbs were never designed to idle) and pull it REAL hard, it will start and run. It just has to play "catch up" with itself. In the auto and motorcycle racing scene, we frequently lighten flywheels (or in some cases with motorcycles leave just the magneto hub) which lets the engine rev faster due to less rotating mass. The reason why we didn't have these problems is there are other cylinders on a different stroke to make up for the loss of momentum. Single cylinder engines will def idle weird like they have a cam with severe overlap.